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Amusing observation...
I disconnected a bunch of microsprinklers from zone13 and got the gpm down to 30. Figured I'd hook up the microsprinklers to the zone with only 2 heads. So I did that. Then went to the water meter to measure the flow rate. Sprinklers on. No flow. Finally realized that the house builder had decided that as the valve was right next to the neighbour's water meter he might as well hook up to their water. But our house was closer, so we get to control it. Very strange. I guess its ok as it is for a planter which is at the side of a shared access lane. Decided to disconnect the extra sprinklers though

For 6-foot-wide strips, there aren't many, if any, nozzle choices. Hunter center-strip nozzles claim a 5x30 pattern, and might do more with higher pressures. Keep working at reducing flow, where possible. The zone with just a couple of heads might be able to be switched over to another existing zone, if the watering times permit. The ICC controller can handle the electrical load of two zone valves at once, along with a possible future master valve. 30 gpm is the target I gave based on the pipe sizes you mentioned. The more you can reduce the system flows, the less water hammer the valves will get, and the more pressure headroom you will have for future changes. Especially if you install a master valve and an RPZ. Lower flows might allow a more economical size of backflow preventer.

Back Again with an update (if anyone's interested Maybe someone will tell me if I'm being dumb anywhere here...
I've been following Wet's recommendation of a long hard look at the system, particularly at balancing flow as the first step of fixing things - lets call this phase 1 of the project Conclusion is that most of the excessive flow rates are due to inappropriate replacement of heads...
Zone 12: Flow rate is 45gpm. Original heads are Toro 570 with 12' half-circle nozzles - 1.09gpm @30psi, spacing 10ft on a 9ft wide bit of grass. 13 of 28 heads have been replaced with nasty brass popups, flowing &gt;2.5gpm. Math tells me that if I replace the brass popups with the same heads as original, I'll be back at 30gpm. Though I may use rainbird 1803 sams on 3 of them, which are on a narrower strip of grass (6ft) running downhill. These are spaced wider (12') than the heads on the main part. 6ft strip with 12' spacing tells me I should try strip heads.
Zone 9: FLow rate is 56gpm. Entirely due to being afflicted with the nasty brass popups. Easy fix with either 570s or 1803s.
Zone 13: Flow rate 75gpm. Can of worms. Appears to have originally had 22H-SS streamers at top and bottom of steep slope. Half appear to have been replaced with an assortment of home-center impact and gear rotors. So far, I've retired the impacts and renozzled the Orbits and KRains to smallest nozzles - somewhere in the .5 to .75gpm area. Result? Original head pressure was 40psi. After changes, pressure went up to 60psi, flow remained at 75gpm. So I used the valve flow control (which I guess keeps me on-topic for this forum) to bring head pressure back down to 40psi, and that got flow down to 45gpm. A major improvement, but not yet where I need to be. I spy a number of nasty brass shrub heads lurking where 22H-SS used to be, so I'll look at those next. At this point I don't know whether I'll get to 30gpm, or whether I'll need to split the zone.
Well, off I go shopping for 570s. Sprinkler warehouse don't seem to carry the 3" ones
- de

A 1&frac12; inch meter has no problem supplying the 75gpm you mentioned. Now, if adding atmospheric vacuum breakers can be done, with the needed elevation above the sprinkler heads they require, that can put the entire system under proper backflow protection. The only other problem I see is how a master valve would be located, if part of the system is fed through a PVB and part of it is fed around it. Nothing a PVB feeds can be within a foot of elevation of the PVB. You cannot have any pipes running uphill from it.

I would still be looking at the possibility of swapping nozzles on rotor heads, if doing so would reduce the flow in the marginal zones (while maintaining coverage) - as far as pressure drop goes, reducing flow rates where you can will allow for some headroom for changes, and maybe even pressure regulation.

You should really locate any missing pieces of the system, especially the line that feeds the four zones that aren't backflow protected. You would like to have a common shutoff for the entire system, and maybe even common backflow protection and pressure regulation.

As for pressure loss for a master valve, you can do much better than 8 psi. The mix of high-flow and low-flow zones on one line force you to use a valve that doesn't have a minimum flow requirement. Standard valves don't have this capability. Nothing sold by Rainbird or Hunter does. You have to stray out of the usual to get a valve that doesn't have a minimum flow requirement. Once you find one, you can use a large enough one to keep pressure loss to a minimum. In your case, with a 75 (or even 50) gpm flow, you'd be using a 2 inch valve, and bushing down the inlet and outlet, if need be. Same thing if you need to put an AVB onto the 75 gpm zone. You'd use a 2 inch one, regardless of the smaller pipe sizes it may connect to.

Before I'd be paying over $250 for what is almost surely a special-order valve, I'd be trying to rework the system to reduce flows and get some extra pressure for the marginal zones. If you could manage to get the flow down to 30 gpm tops, you'd have a much healthier system. Too much water rushing through too small a pipe results in surge pressures and water hammer that can make perfectly good valves into leakers. The Hunter controller can supply power for additional zones, if need be, by adding a module, and it looks like you have a zone or two you aren't making full use of.

Give the whole system a good hard look before you spend more money on it.

Yes I 100% agree, its a screwed up system. If I knew 6 years ago how many problems I would have, it would have been replaced. I omitted to mention how several zones water both grass and flower beds.
Regarding the slope, most of the property is level, with a short 45degree downslope at one end, and a short 45deg upslope at the other. The zones on both slopes are those not served by the PVB. I suspect the easiest fix for this is to move the valves to the top of the slope and use atmospheric backflow valves. I rechecked the water meter, its definitely 1.5inch. Anyhow, I plan to take your advice and fix the system properly, with reconfigured zones. What master valve do you suggest? Would something like a Rainbird GB work for this? Its got about 8psi drop at 50gpm.
Thank you for taking the time to offer your advice - much appreciated.
David

Sixteen zones? For a simple solution, install a brass master valve you can trust, and the pressure stops there. If you need to open some remote faucet on the mainline for water, you can turn on the disabled zone to pressurize the mainline. I know of one brass electric valve that will have a minimal pressure loss, due to its special design and solenoid. It will cost you more than $250

But basically, this sounds like a screwed-up system, if it's using such a wide range of flow-rates, with some of it not being backflow-protected. By the way, the maximum rated flow for a one-inch water meter is supposed to be 50 gpm, according to AWWA standards.

The real solution is to break it down into more evenly matched zones that can run at lower pressures, and to regulate the pressure upstream of the entire system. Also, if the property runs uphill from the house, you should know that the PVB only provides backflow protection for those sprinklers that are lower in elevation than the PVB. The one device that can protect the entire system, at any and all elevations, according to California code, is an RPZ device. An RPZ has a 10 to 15 psi pressure loss, so making the system right will require some reconfiguration, if some zones are really marginal. Often, you can swap out sprinkler-head nozzles, and balance things out.

Hi wetboots.
Property is 1 acre, in southern california - no freezing. 16 zones. Zone gpm is (for zones 1 to 16) 0, 31, 14, 19, 30, 45, 18, 25, 56, 20, 0, 45, 75, 30, 30, 17. (zone 1 is disabled, zone 11 is only 2 heads so too low to bother measuring). Zones 11 thru 15 are fed direct from incoming water main - appears to be 1.25in pvc at first valve, 1" at others. Other zones are through PVB near house. Probably installed at different times. Main line to/from PVB is 1.5inch. Water meter is labelled 1 to 1.5", line is definitely bigger than 1" so probably 1.5". Controller is Hunter ICC. Have 1 zone which is marginal pressure at end and cannot tolerate any pressure reduction. This is fixable as it is 26 heads over 200ft of 1" with a 12ft rise in height. Valve is at _far_ end with 1" line running out to valve. Could easily be fed mid-way by moving valve back to the 1.25" line. But it all consumes time
Thanks!

How large is the property? Where (freezing northern climate, or warm southern area) is it? How many zones are there? What is the mainline pipe size? Water meter size? How many gpm in a zone? More details might result in more specific suggestions.